Powering an undocumented SBC

I've come into the possession of a quaint little single-board Z80 using a pretty standard chipset (Z84C Serial interface chip, PIO, CPU, CTC) and some basic RAM (Motorola 256KByte chip, M5M5256DP-70LL), and I'd like to power this little board, seeing as it has some cool functions (Direct interface to a board with an alphanumeric VFD and 4x4 keypad and a Bell 212A modem) However, this is where the problem is. The board really has no indication on it's pin header (12 pins) where it hides the power and ground. I tried using my multimeter to continuity check power pins on the board, but is this the method I'm stuck with?

hi,
The Z80 series and that EPROM are +5V/0V powered.
On the EPROM pin12 is 0V and pin24 is +5V
The 0V rail should be common throughut the pcb

You should be able to work back towards the power input to the pcb.
The pcb also has a RTC with battery backup.

The photo is out of focus, so I cannot identify some parts...

Humm, looks like many modem type products. I suspect the power input might be that four pin connector in the upper right of the pic. Many modem used AC wall wart power modules that it looks like the upper right input components might be rectifier components to convert to DC. Many used around 8vac as a input power source. So you might have to reverse engineer the components in the upper right hand corner and see it it's the power source for this PCB assembly.

Good luck

Lefty

The upper right corner of the board (P2) is the phone line interface. Notice that the whole section is lighter color (no internal ground plane). There are 3 opto isolators (6 pin chips), a transformer and a relay that span from the phone interface to the main part of the board. There's not anything that looks to me like a regulator, so I expect that there are pins extending downward from P1 (upper left) that get 5.0V from a host board of some kind. As previously mentioned, ringing out the + and 0V pins from any known chip will produce the pin out.

What do P3 and P4 look like from the side view?

Actually, the board is from a Verifone terminal from the 90's, hence the modem chip. The chips are as follows:
Zilog Z84C4006PEC (Serial Interface)
Zilog Z84C2006PEC (PIO)
Zilog Z84C0006PEC (Z80)
Zilog Z84C3006PEC (Counter/Timer)
TDK 73K222AL-IP (Bell 212A modem)
ST M27C256B (UV-erasable EPROM, 256Kbyte)
Motorola M5M5256DP-70LL (RAM)
Along with some lesser chips like an octal buffer/line driver, some optoisolators, and probably importantly, a NatSem LM3578AN switching regulator. The rest of the board is pretty simple, upper-right is support circuitry for the modem (I'm guessing this includes the transformer) and ports for RS232 and some other proprietary connector.

Here's the P3 and P4 connectors side-on, for those who are interested.